The present invention relates to a spindle motor and, in particular, to a bearing assembly of such a motor.
A spindle motor in general comprises a stator and a rotor, including a hub for supporting an optical or magnetic disc or the like. A bearing assembly is provided between the stator and the rotor and consists of a journal bearing and a thrust bearing. It is known to provide both the thrust and journal bearings as hydrodynamic bearings. However, lubricant used in such bearings can be somewhat difficult to seal and may contaminate the recording medium of the disc mounted to the rotor if fluid migration from the bearing occurs. Hydrodynamic bearings also have a disadvantage of high frictional losses during operation.
Aerodynamic bearings may be utilised instead of hydrodynamic bearings, to reduce frictional losses and allow for increased operating speeds, however, aerodynamic bearings have relatively low bearing stiffness.
A spindle motor, as disclosed in U.S. Pat. No. 4,200,344, ameliorates the above disadvantages by using a liquid lubricant for the journal bearing only and providing an aerodynamic for the thrust bearing. However, the thrust bearing is only adapted to function in a uni-directional manner, which is not desirable for practical disc drives.
U.S. Pat. No. 5,358,339 also discloses a spindle motor with a liquid journal. That motor includes two flat thrust plates at either end of the journal bearing to thereby provide for bi-direction axial support. A disadvantage of such a motor though is that the thrust plates, which need to be of a sufficient size to generate suitable aerodynamic pressure to form a gas bearing, increase the overall volume dimension and space requirements of the motor.
The present invention seeks to address the above mentioned disadvantages.
In accordance with the invention, there is provided a spindle motor including a stator component, a rotor component, including a hub for supporting one or more discs, and a bearing assembly between the components, formed of a journal bearing and a thrust bearing, wherein the journal bearing is an aerodynamic bearing and the thrust bearing is adapted to function in a bi-directional manner and includes an annular member projecting radially from one of the components into an associated recess formed in the other of the components.
Preferably, the journal bearing is formed between a shaft of one of the components and an associated sleeve of the other one of the components and the shaft is provided with a passage extending therethrough for providing air flow through the motor to the aerodynamic bearing, so as to allow air to be entrained into the journal bearing during operation.
Preferably, the annular member has two opposed bearing faces arranged adjacent corresponding bearing surfaces of the recess, and a hydrodynamic bearing is formed between the respective bearing faces and surfaces.
Preferably, the bearing surfaces diverge from the bearing faces adjacent the shaft so that liquid between the annular member and the recess is retained therebetween by surface tension seals.
Preferably, the shaft includes a thrust bearing passageway which includes a port opening adjacent the annular member, between the thrust bearing and the journal bearing for equalising air pressure at either side of the journal bearing.
Preferably, the shaft is fixed relative to the stator and the sleeve forms part of the rotor.